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Chapter 3 Outline Adverse reactions Definitions and classifications Clinical manifestations of adverse reactions Toxicologic evaluation of drugs Chapter 3: Adverse Reactions Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Adverse Reactions Adverse Reactions Haveles (p. 28) Drugs may act on biologic systems to accomplish a desired effect, but they lack absolute specificity 2 No drug is free from producing some adverse effects in a certain number of patients They can act on many different organs or tissues This is the reason for undesirable or adverse drug reactions Estimates indicate that between 5% and 10% of patients hospitalized in the Unite States are admitted because of adverse reactions to drugs cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 3 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Definitions and Classifications Definitions and Classifications Haveles (pp. 28-29) (Fig. 3-1) Every drug has more than one action 4 Adverse reactions may be divided into the following categories Toxic reaction: an extension of the pharmacologic effect resulting from a drug’s effect on the target organs • The amount of the desired effect is excessive Side effect: a dose-related reaction that is not part of the desired therapeutic outcome • The drug acts on nontarget organs to produce an Therapeutic effects are clinically desirable actions Adverse effects are clinically undesirable reactions • Not desired, potentially harmful, and occurs at usual therapeutic doses undesirable effect cont’d… cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 5 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 6 1 Clinical Manifestations of Adverse Reactions Definitions and Classifications Idiosyncratic reaction: a genetically related abnormal drug response Drug allergy: an immunologic response to a drug resulting in a reaction such as rash or anaphylaxis • Neither predictable nor dose related Interference with natural defense mechanisms • The drug reduces body’s ability to fight infection Haveles (pp. 29-31) Exaggerated effect on target tissues Effect on nontarget tissues Effect on fetal development (teratogenic effect) Local effect Drug interactions Hypersensitivity (allergic reaction) Idiosyncrasy Interference with natural defense mechanisms cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 7 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Clinical Manifestations of Adverse Reactions Exaggerated Effect on Target Tissues Haveles (p. 29) Before a drug is used, its risk against its benefits must be assessed The beneficial effect must be weighed against its potential for adverse reactions Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Haveles (p. 29) An extension of therapeutic effect caused by the overreaction of a sensitive patient or by a dose that is too large for that patient 9 Occasionally, this may result from liver or kidney disease Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 10 Effect on Fetal Development (Teratogenic Effect) Effect on Nontarget Tissues 8 Haveles (p. 29) Caused by the nontherapeutic action of the drug Reactions can occur at usual doses but appear more often at higher doses A reduction in dose usually reduces these adverse reactions Haveles (pp. 29-30, 491) (Table 25-2) The relationship between drugs and congenital abnormalities has been recognized since the middle of the twentieth century “Although more information is now available about the safety of drugs in pregnant women, sufficient information is still lacking” The U.S. Food and Drug Administration (FDA) has attempted to address concerns about the lack of adequate knowledge of drugs by defining five FDA pregnancy categories They are A, B, C, D, and X (from least to most risky) cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 11 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 12 2 Effect on Fetal Development (Teratogenic Effect) Although no drug can be considered “safe” for administration to a pregnant woman, many of the drugs used in dentistry are among the safest Local Effect Occasionally, injectable drugs can produce irritation, pain, and tissue necrosis at the site of injection Topically applied agents can produce irritation at the site of application Drugs taken orally can produce gastrointestinal symptoms such as nausea or dyspepsia These drugs include penicillin and erythromycin, acetaminophen, and the local anesthetic lidocaine Drugs used in dentistry contraindicated for pregnant women include tetracycline, nonsteroidal antiinflammatory agents, benzodiazepines, and metronidazole Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 13 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Haveles (p. 30) A drug interaction can occur when the effect of one drug is altered by another drug 14 Hypersensitivity (Allergic Reaction) Drug Interactions Haveles (p. 30) Local reactions are characterized by local tissue irritation Interactions may result in toxicity or lack of efficacy Interactions may also produce beneficial effects Haveles (pp. 30-31) Occurs when the immune system of an individual responds to the drug administered or applied The drug must act as an antigen and stimulate antibody production in a previously sensitized patient Neither dose dependent nor predictable The likelihood that a drug interactions would occur increases with the number of drugs a patient is taking cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 15 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Hypersensitivity (Allergic Reaction) Hypersensitivity (Allergic Reaction) An ingested drug may be metabolized to a reactive metabolite known as a hapten The hapten can act as an antigen after combining with proteins in the body The antigen formed then stimulates the production of an antibody 16 Haveles (pp. 30-31) (Table 3-1) Drug allergy can be divided into four types of reactions, depending on the type of antibody produced or the cell mediating the reaction With subsequent exposure to the drug, the antibodies formed will react with the antigen (drug or metabolite) administered and elicit an antigen-antibody reaction cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 17 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 18 3 Type I (Immediate) Type I (Immediate) Mediated by immunoglobulin E (IgE) antibodies When a drug antigen binds to IgE antibody, histamine, leukotrienes, and prostaglandins are released, producing vasodilation, edema, and inflammation The targets of this reaction are • Bronchioles, resulting in anaphylactic shock • Respiratory system, resulting in rhinitis and asthma • Skin, resulting in urticaria and dermatitis Because these reactions can occur quickly after drug exposure, they are known as immediate hypersensitivity reactions Anaphylaxis is an acute, life-threatening allergic reaction characterized by hypotension, bronchospasm, laryngeal edema, and cardiac arrhythmias cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 19 Complement-dependent reactions involving either immunoglobulin G (IgG) or immunoglobulin M (IgM) antibodies Mediated by IgG antibodies The drug antigen-antibody complex fixes complement and deposits in the vascular endothelium Manifested as serum sickness; includes urticarial skin eruptions, arthralgia, arthritis, lymphadenopathy, and fever Can be caused by penicillins and sulfonamides The antigen-antibody complex is fixed to a circulating red blood cell, resulting in lysis Examples are penicillin-induced hemolytic anemia and methyldopa-induced autoimmune hemolytic anemia Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 21 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Type IV (Delayed Hypersensitivity) 22 Idiosyncrasy Mediated by sensitized T lymphocytes and macrophages When the cells contact the antigen, an inflammatory reaction is produced by lymphokines, neutrophils, and macrophages An example is contact dermatitis caused by topical application of drugs Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 20 Type III (Immune complex/Arthus/Serum sickness) Type II (Cytotoxic/Cytolytic) Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 23 Haveles (p. 31) A reaction that is neither the drug’s side effect nor an allergic reaction Some are genetically determined abnormal reactions; others may be the result of an immunologic mechanism Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 24 4 Interference with Natural Defense Mechanisms Toxicologic Evaluation of Drugs Haveles (p. 31) A drug’s effect on the body’s defense mechanisms can result in an adverse reaction Long-term systemic administration of corticosteroids can result in decreased resistance to infection Haveles (pp. 31-32) Evaluations of the toxic effects of drugs are based on experiments performed with lower animals and clinical trials conducted in humans Animal experiments can often elicit adverse reactions that could occur in humans, but drug reactions in animals do not always predict reactions in humans cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 25 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. Toxicologic Evaluation of Drugs 26 Toxicologic Evaluation of Drugs Haveles (p. 31) (Fig. 3-2) The median lethal dose (LD50) is the dose the kills 50% of experimental animals The median effective dose (ED50) is the dose required to produce a specified intensity of effect in 50% of the animals The ratio LD50/ED50 is the therapeutic index (TI) of a drug Haveles (pp. 31-32) (Fig. 3-3) If the value of the TI is small (narrow TI), then toxicity is more likely If the TI is large (wide TI), then the drug will be safer A TI of greater than 10 is usually needed to produce a therapeutically useful drug cont’d… Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 27 Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved. 28 5